A method for controlling a printing control system for controlling scanning of printing means in accordance with the print dot duty in a dot printer is described in Japanese Patent Application Laid-Open No. SH063-188059. In this method, the number of dots to be printed in every dot column in one line is counted, a weight is given in accordance with the counted number of dots, numeric values determined by the weights are accumulated successively and, when the accumulated value exceeds a reference value, that is, when a print dot duty value in one line exceeds the reference value, printing of that line is performed by separating the printing into a plurality of line printing scans.
In the above-described conventional printing control system, divided printing is performed when the print dot duty value exceeds a reference value in response to a decision in the operation of the printing control. The number of divisions in divided printing is fixed. In divided printing, the line is printed with three reciprocating scannings by dividing the number of print dots in the line by 3 when it is difficult to print one column with one reciprocating scanning of the printing means. In the above-mentioned conventional system, however, since the state of print dot duty values is not detected for dot columns after the dot column in which divided printing has been determined, a reduction in the print quality of dot columns after the dot row in which the above-described divided printing has been determined sometimes occurs, depending on setting of the number of reciprocation times in divided printing. Further, printing may be performed without causing any reduction in the print quality if a large number of division times is set during divided printing, but useless printing time is spent in many cases with this arrangement.